1. Field of the Invention
The present invention relates to a magnetic sensor, and more particularly, to a magnetic sensor that uses a spin-filtered sensor current to provide high-density recording and reproduction of information to and from a hard disk or other such magnetic recording medium.
2. Description of Related Art
Computers employing hard disk drives and other magnetic recording and reproduction units continue to require ever greater abilities to record information densely and to reproduce such densely recorded information accurately, which in turn means creating ever more sensitive magnetic sensors.
Specifically, as the recording density of the recording medium increases, the size of the leakage magnetic field (the signal magnetic field) from each bit decreases, which in turn has lead to proposals for magnetic reproduction heads mounting more sensitive sensors capable of detecting these reduced signal magnetic fields.
Conventionally, one well known type of sensor for reproduction heads is the magneto-resistive (MR) sensor employing the magneto-resistive effect. The MR sensor is of two types: an anisotropic magneto-resistive (AMR) film employing an anisotropic magneto-resistive effect, and a giant magneto-resistive (GMR) film which is a multi-layered structure.
A so-called spin-valve structure employing four basic layers is commonly used for the GMR film. The four layers of the spin-valve structure are an anti-ferromagnetic layer, a fixed magnetic layer, a non-magnetic metallic layer and a free magnetic layer.
Many proposals have been put forward to improve this basic structure, involving mainly improvements in the magnetic materials used and in their combination as well as changes in the number of layers used. However, the size of the signal magnetic fields from the ever more densely recorded magnetic recording medium continues to decrease at a rapid rate, such that mere improvements to the materials and structure of the MR sensor described above are unable to keep pace, that is, are unable to guarantee the level of sensitivity required to reproduce accurately the information recorded on the magnetic recording medium.
Accordingly, it is an object of the present invention to provide a new and useful magnetic detector in which the above-described disadvantage is eliminated.
The above-described object of the present invention is achieved by a magnetic sensor that senses an external magnetic field using a spin-filtered sensor current flowing through a non-magnetic layer.
According to this aspect of the invention, the use of a spin-filtered sensor current flowing through a non-magnetic layer provides a magnetic sensor with improved sensitivity.
Additionally, the above-described object of the present invention is also achieved by the magnetic sensor as described above, further having:
a pair of ferromagnetic bodies provided on the non-magnetic layer and positioned parallel to an axis of magnetization of each of the ferromagnetic bodies; and
a power source that uses the ferromagnetic bodies as electrodes to supply the sensor current.
Additionally, the above-described object of the present invention is also achieved by the magnetic sensor as described above, wherein:
a ferromagnetic film is provided on the non-magnetic layer; and
an axis of magnetization of the ferromagnetic layer is formed either parallel to or opposite to a direction of electron spin of the sensor current.
Additionally, the above-described object of the present invention is also achieved by the magnetic sensor as described above, wherein the ferromagnetic layer is formed as a free layer constituting either an anisotropic magneto-resistive film or a giant magneto-resistive film.
Additionally, the above-described object of the present invention is also achieved by the magnetic sensor as described above, wherein:
the non-magnetic layer is formed of a semiconductor material; and
the axis of magnetization of one of the pair of ferromagnetic bodies changes so as to detect an external magnetic field.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.